The present invention relates to a steering wheel pad attachment structure and, more particularly, to a steering wheel pad attachment structure in which side walls of the pad are connected to side walls of a bag holder of an air bag device.
A conventional steering wheel pad of an air bag device has, for example, the following attachment structure. As shown in FIG. 12, an air bag holder 51 comprises a main body 51a having an opening formed in the center, and side walls 51b extending downwardly, as viewed in the figure. As a whole, the bag holder 51 has, for example, a box-like shape. The bag holder 51 is secured on bosses (not shown), and an inflator 52 is provided in the above-mentioned central opening. Also, an air bag 53 made of cloth and a ring retainer 54 are attached to the upper surface of the bag holder 51. Further, a steering wheel pad 55 (hereinafter referred to simply as "pad") is provided over the bag holder 51.
The pad 55 comprises a pad main body (not shown) which covers an upper portion of the bag holder 51, and pad side walls 56 which extend substantially perpendicularly (downwardly, as viewed in the figure) from a periphery of the pad main body toward the bag holder 51. Holes 57 and 58 are formed in the side walls 51b of the air bag holder 51 and the pad side walls 56, respectively. The holes 57 and 58 are aligned with each other in such a manner that the pad side walls 56 abut against the side walls 51b of the air bag holder 51. Side walls 51b and 56 are fastened to one another with rivets 59. The pad 55 is thus fixedly attached to the air bag holder 51.
When the air bag 53 is inflated, the pad side walls 56 undergo large outward stresses. Accordingly, the pad side walls 56 can break or tear at the holes 58 due to the stresses. Therefore, support plates 60 having recesses 60a are conventionally provided on the outer surface of the pad side walls 56. The side walls 51b and 56 are then fastened with rivets 59. With such a structure, even if the pad side walls 56 experience outward stresses, tearing of the pad side walls 56 can be prevented by frictional force between pad side walls 56 and the support plates 60, and by engagement between the recesses 60a and the pad side walls 56.
In the conventional technique described above, however, various kinds of additional parts, such as rivets 59 and support plates 60, are required to attach the pad 55, thereby increasing the costs for such attachment. In order to solve such cost problems, for example, a structure as disclosed in Japanese Utility Model Unexamined Publication No. 63-189962 is known. In this structure, as shown in FIG. 13, a number of claws 62 are provided at the outer periphery of an air bag holder (base plate) 61. Also, curved engaging tongues 63, which have a substantial U-shape, are provided adjacent to the outer peripheral portion of the air bag holder 61. Further, holes 64 are formed in distal end portions of the engaging tongues 63 at positions corresponding to the claws 62. When a pad 65 is attached, holes 67 in pad side walls 66 receive the claws 62, and the engaging tongues 63 are bent inwardly. Then, the holes 64 in the distal end portions of the engaging tongues 63 are engaged with the claws 62. With this engagement, the pad 65 is fixed on the bag holder 61.
Moreover, with such an attachment structure, additional members, such as rivets and support plates mentioned above, are unnecessary, so manufacturing costs can be reduced. Furthermore, when the claws 62 are particularly dimensioned, outwardly directed inflation-related stresses can be dispersed even if such stresses are exerted on the pad 65. Consequently, breaking or tearing of the pad side walls 66 can be prevented. However, if such stresses are exerted laterally (to the left in the figure), claws 62 may come disengaged from the holes 67, making it impossible to maintain the engagement therebetween. In other words, the pad 65 undergoes outward and lateral stresses when the air bag is inflated, and the pad 65 may be detached from the bag holder 61 because of such stresses.